Methods for making products of natural or artificial latex rubbers are known in the prior art. Such methods include a dipping stage whereby a mould is dipped in liquid latex, or a press stage. In order to build up the latex to a desired thickness and to reduce the product stickiness, several known techniques are used. Examples of such techniques are based, for instance, on the use of coagulants to control the thickness, diatomite earth products as releasing agent and heating of the mould to build up a thicker layer of latex.
However, prior techniques for making products from natural or artificial latex have a number of disadvantages. For instance, such techniques result in products that are often very thin or very thick and are useless wherein a non-rubber tactile surface feeling is desired, particularly for products that touch skin. In addition, prior techniques do not easily allow for releasing and stripping of very thin products from their moulds without damaging the products. Liquid and gas jets have been used to separate products from their mould, for example, stripping balloons, gloves, and the like. However, the use of liquid and gas jets is inadequate to remove products that are massively perforated before removal from their moulds. Moreover, prior separation techniques are useless for removing protective garments and bandages which may include absorptive pads as the pad might be damaged.
It is also difficult to control the thickness of latex products using conventional techniques. For instance, traditional dipping methods involve a mould and a dipping tank wherein the mould is dipped in the dipping tank either in a vertical movement or in a circular movement towards the liquid latex contained in the tank. A major disadvantage of the dipping method is that when a large mould is dipped into the tank, it is almost impossible to keep all parts of the mould dipped for the same amount of time because the parts dipped first come out last. This disadvantage is not eliminated by the diagonal dipping technique and it is very difficult to achieve a latex layer with even thickness. In addition, it is also impossible to selectively control the thickness of the layers and to create areas having different thicknesses in the final product. For example, it is difficult or impossible to make products such as protective undergarments wherein the thickness of the waist and leg openings are different than that of other parts of the garment.
A further disadvantage of the dipping methods is air bubbles forming along the surface of the mould and getting trapped underneath the mould. This causes unwanted holes and damage to the surface area of the product.
The delicate, and therefore slow, process of dipping as known in the art, makes the methods time consuming, more so when relatively large or complex shaped three dimensional moulds are employed.
A further disadvantage of the dipping method is that it forces the dipping of the whole mould, thereby not allowing the cover of specific required locations, causing waste in product material.
Furthermore, it is known in the art that latex products may be coated with natural or synthetic fibres in order to create a smooth and cosy feeling for the wearer, particularly where protective garments are involved. The fibres are “flocked” over a sticky layer of latex or adhesive on the latex. However, in order to coat a product on both sides, the steps of stripping the cured latex products from the former and refitting them on the former for coating the second surface of the product are needed and several layers of latex and/or adhesive must be applied to allow the fibres to adhere. Thus, methods known in the art for coating latex products with fibres result in increased product thickness and require complex manufacturing processes.
Accordingly, methods are needed to overcome the above-mentioned disadvantages. In particular, methods are needed to remove products from their moulds without damaging the products; to apply loose fibres easily to products on one or both sides; to generate perforations in the product without the need for stripping the product first or making additional steps; and to create products with uniform or varying thickness in a controlled manner. Thus, the present invention provides methods that overcome the above-mentioned disadvantages and result in products that can be efficiently perforated and efficiently removed from their moulds. In addition, the methods of the invention provides ways to efficiently apply double-sided fibre coatings to products and to create products with varying thickness in a controlled manner.